1. Field of the Invention
The present invention relates to multi-band wireless communication systems, and particularly to a four element reconfigurable MIMO antenna system for a cognitive radio platform for compact wireless devices and LTE mobile handsets.
2. Description of the Related Art
In modern wireless communications, the exponential growth of wireless services results in an increasing demand of the data rate requirements and reliability of data. These services may include high-quality audio/video calls, online video streaming, video conferencing and online gaming. These demanding features may require wide bandwidth to cover operation across several frequency bands. This provides motivation towards the comprehensive and efficient utilization of the available spectrum. The desire to overcome inefficient and highly underutilized spectrum resources has led to the concept of cognitive radio (CR). A CR system is based on structural design of a software-defined radio intended to enhance spectrum utilization efficiency by interacting with the operating environment. A CR-based system must be aware of its environment by sensing spectrum usage and have the capability to switch over the operating points among different unoccupied frequency bands. A CR-based system may have various features, including sensing the spectrum of nearby devices, switching between different frequency bands, and power level adjustment of transmitting antennas.
Reconfigurable antennas are able to change their operating fundamental characteristics, e.g., resonant frequency, radiation pattern, polarization, and impedance bandwidth. A frequency reconfigurable antenna is an essential component of CR platforms. An attractive feature of such an antenna is the ability to switch across several frequency bands by activating different radiating parts of the same antenna. CR-based systems are capable of switching the frequency bands of a single frequency reconfigurable antenna over different bands to efficiently and inclusively utilize the idle spectrum.
To achieve the desired characteristics of reconfigurability and the desired performance of a MIMO antenna system, several challenges need to be overcome. These issues include the size of the antennas for low frequency bands, the high isolation required between closely spaced antennas, and control circuitry embedded within the given antenna size to achieve the desired reconfiguration. The performance of a MIMO system degrades significantly for closely spaced antennas due to high mutual coupling.
Thus, a four element reconfigurable MIMO antenna system solving the aforementioned problems is desired.